1. Field of the Invention
The present invention relates to a packet converting apparatus and method, and more particularly, to a packet converting apparatus and method that converts the data packet of various types used in communication networks.
2. Description of the Related Art
For efficient communication of an audio signal, a transmitter part converts an analog audio signal to a digital signal and compresses the digital signal through a vocoder. A receiver decodes the compressed digital signal to restore audio and again converts the audio signal to the analog signal. Such a function is implemented by the vocoder. The vocoder has been developed in various aspects according to purpose of use and field of application services. The vocoder is also used for storage, such as a voice inbox and for communication.
A related art packet converting apparatus and method in communication systems using different vocoders is shown in FIG. 1 which illustrates a general cable/radio communication network.
The cable/radio communication network, as shown in FIG. 1, includes a mobile network 50, a public switched telephone network (PSTN) 60, and an Internet protocol (IP) network 70.
In communication based on the mobile network 50, EVRC/AMR 10 protocal, such as IS-127, v8 Kbps EVRC, GSM v12 Kbps AMR, IS-96 v8 Kbps QCELP, IS-733 v13 Kbps QCELP, and GSM 13 Kbps FER, are used. In communication based on the PSTN 60, G.711(PCM) 20 and 32 Kbps G.726 are used. In communication based on the IP network 70, 6.3/5.3 Kbps G.723.1 and 8 Kbps G729 30 are used.
Therefore, an apparatus for converting an audio packet of different types is required between communication systems using different vocoders. Such media conversion is implemented through a media gateway 40 shown in FIG. 1.
FIGS. 2 and 3 are block diagrams of a related art packet converting apparatus (media gateway) for describing a related art packet converting method. In FIG. 2, a tandem encoding method is used as a packet converting method. In the tandem encoding method, a packet of a first type encoder 80 received through a first network 90 is decoded by a first type decoder 41 of the media gateway 40 so that a PCM signal is obtained. The PCM signal is again encoded by a second type encoder 44 to obtain a desired packet. For example, the decoded PCM signal is analyzed by the second type encoder 44 to obtain encoded parameters. The encoded parameters are then quantized and packed so that the packet data is transmitted to a second type decoder 110 of the receiving party through a second network 100.
FIG. 3 illustrates the reverse of FIG. 2, and thus the description will be omitted.
FIGS. 4 and 5 illustrate a related art packet converting method. FIG. 4 illustrates a tandem coding method in which Packet-A of the first type decoder 41, received in the media gateway 40, is converted to a second type packet in the encoder 44.
Referring to FIG. 4, an audio packet of the first type encoder 80, input through the first network 90, is bit-unpacked in the first type decoder 41 (S10). Subsequently, the unpacked data is inverse quantized so that an audio parameter of the first type encoder 80 is obtained (S11). PCM type audio signals are synthesized using the audio parameter (S12). Then, the first type decoder 41 transmits the PCM audio signals to the second type encoder 44, and the second type encoder 44 analyzes the received PCM signals to obtain an audio parameter of the second type packet (S13). The audio parameter of the second type packet is then quantized (S14). The quantized data is bit-packed so that a second type audio packet is output to the second type decoder 110 through a second network 100 (S15).
FIG. 5 illustrates a tandem coding method in which a packet Packet-B of the second type decoder 46, received in the media gateway 40, is converted to a packet of the first type encoder 47. Referring to FIG. 5, an audio packet of the second type encoder 130, input through the second network 100, is bit-unpacked in the second type decoder 46(S20). Subsequently, the unpacked data is inverse quantized so that an audio parameter of the second type encoder 110 is obtained (S21). PCM type audio signals are synthesized using the audio parameter (S22). Then, the second type decoder 46 transmits the PCM audio signals to the first type encoder 47, and the first type encoder 47 analyzes the received PCM signals to obtain an audio parameter of the first type packet (S23). The audio parameter of the first type packet is then quantized (S24). The quantized data is bit-packed so that a first type audio packet is output to the first type decoder 140 through the first network 90 (S25).
The aforementioned related art packet converting apparatus and method has several problems. After the PCM signals are generated inside the media gateway, complicated steps are performed in such a manner that the parameter is analyzed and quantized using the PCM signals as input signals of a desired encoder. Such steps increase signal processing time and quantity. For parameter analysis, a delay corresponding to a frame length of the encoder, including lookahead delay additionally occurs. Such problems constrain the number of channels of a multi-channel real time packet converting apparatus in the media gateway. This constrains the number of subscribers to the mobile network and the IP network.